﻿/*
 * Copyright (c) 1982, 1986, 1988, 1990, 1993
 *	The Regents of the University of California.  All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 * 3. All advertising materials mentioning features or use of this software
 *    must display the following acknowledgement:
 *	This product includes software developed by the University of
 *	California, Berkeley and its contributors.
 * 4. Neither the name of the University nor the names of its contributors
 *    may be used to endorse or promote products derived from this software
 *    without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
 * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
 * SUCH DAMAGE.
 *
 *	@(#)uipc_socket.c	8.3 (Berkeley) 4/15/94
 */

#include <sys/param.h>
#include <sys/systm.h>
#include <sys/proc.h>
#include <sys/file.h>
#include <sys/malloc.h>
#include <sys/mbuf.h>
#include <sys/domain.h>
#include <sys/kernel.h>
#include <sys/protosw.h>
#include <sys/socket.h>
#include <sys/socketvar.h>
#include <sys/resourcevar.h>

/*
 * Socket operation routines.
 * These routines are called by the routines in
 * sys_socket.c or from a system process, and
 * implement the semantics of socket operations by
 * switching out to the protocol specific routines.
 */
/*ARGSUSED*/
socreate(dom, aso, type, proto)
	int dom;
	struct socket **aso;
	register int type;
	int proto;
{
	struct proc *p = curproc;		/* XXX */
	register struct protosw *prp;
	register struct socket *so;
	register int error;

	if (proto)
		prp = pffindproto(dom, proto, type);
	else
		prp = pffindtype(dom, type);
	if (prp == 0 || prp->pr_usrreq == 0)
		return (EPROTONOSUPPORT);
	if (prp->pr_type != type)
		return (EPROTOTYPE);
	MALLOC(so, struct socket *, sizeof(*so), M_SOCKET, M_WAIT);
	bzero((caddr_t)so, sizeof(*so));
	so->so_type = type;
	if (p->p_ucred->cr_uid == 0)	/* 如果调用socket()的进程有管理员权限，设置SS_PRIV标志 */
		so->so_state = SS_PRIV;
	so->so_proto = prp;
	error =
	    (*prp->pr_usrreq)(so, PRU_ATTACH,
		(struct mbuf *)0, (struct mbuf *)proto, (struct mbuf *)0);
	if (error) {
		so->so_state |= SS_NOFDREF;
		sofree(so);
		return (error);
	}
	*aso = so;
	return (0);
}

sobind(so, nam)
	struct socket *so;
	struct mbuf *nam;
{
	int s = splnet();
	int error;

	error =
	    (*so->so_proto->pr_usrreq)(so, PRU_BIND,
		(struct mbuf *)0, nam, (struct mbuf *)0);
	splx(s);
	return (error);
}

solisten(so, backlog)
	register struct socket *so;
	int backlog;
{
	int s = splnet(), error;

	error =
	    (*so->so_proto->pr_usrreq)(so, PRU_LISTEN,
		(struct mbuf *)0, (struct mbuf *)0, (struct mbuf *)0);
	if (error) {
		splx(s);
		return (error);
	}
	if (so->so_q == 0)	/* 如果当pr_usrreq返回时有连接正在连接队列中，则不设置SO_ACCEPTCONN标志。 */
		so->so_options |= SO_ACCEPTCONN;
	if (backlog < 0)
		backlog = 0;
	so->so_qlimit = min(backlog, SOMAXCONN);	/* 设置监听socket维护连接队列容量 */
	splx(s);
	return (0);
}

sofree(so)
	register struct socket *so;
{
	if (so->so_pcb || (so->so_state & SS_NOFDREF) == 0)	/* 要释放的socket没有解绑协议控制块，终止释放操作 */
		return;

	if (so->so_head) {	/* 如果插口仍在连接队列上 (so_head非空)，则清空socket队列，否则内核panic出错 */
		if (!soqremque(so, 0) && !soqremque(so, 1))
			panic("sofree dq");
		so->so_head = 0;
	}
	sbrelease(&so->so_snd);	/* 释放发送缓存数据 */
	sorflush(so);			/* 释放接收缓存数据 */
	FREE(so, M_SOCKET);		/* 释放socket结构本身 */
}

/*
 * Close a socket on last file table reference removal.
 * Initiate disconnect if connected.
 * Free socket when disconnect complete.
 取消socket上所有未完成的连接 (即，还没有完全被进程接受的连接 )，等待数据被传输到外部系统，释放不需要的数据结构。
*/
soclose(so)
	register struct socket *so;
{
	int s = splnet();		/* conservative */
	int error = 0;

	/* 如果插口正在接收连接，遍历两个连接队列调用 soabort取消每一个挂起的连接。这种情况只会发生在监听socket的情况 */
	if (so->so_options & SO_ACCEPTCONN) {
		while (so->so_q0)
			(void) soabort(so->so_q0);
		while (so->so_q)
			(void) soabort(so->so_q);
	}

	/* 协议控制块为空，则协议已同插口分离，直接退出 */
	if (so->so_pcb == 0)
		goto discard;

	/* 断开已建立的连接或关联 */
	if (so->so_state & SS_ISCONNECTED) {
		if ((so->so_state & SS_ISDISCONNECTING) == 0) {		/* 如果断连没有开始，则 sodisconnect启动断链 */
			error = sodisconnect(so);
			if (error)
				goto drop;
		}
		if (so->so_options & SO_LINGER) {
			if ((so->so_state & SS_ISDISCONNECTING) &&
			    (so->so_state & SS_NBIO))	/* 如果设置了SO_LINGER选项，但socket是非阻塞的无需等待断链完成直接退出 */
				goto drop;

			/* 如果设置了SO_LINGER选项且socket是阻塞的，必须等待以下任一事件发生才能完成操作
			  1.断连完成
			  2.拖延时间(s o _ l i n g e r)到
			  3.进程收到了一个信号
			*/
			while (so->so_state & SS_ISCONNECTED)
				if (error = tsleep((caddr_t)&so->so_timeo,
				    PSOCK | PCATCH, netcls, so->so_linger))
					break;
		}
	}
drop:
	if (so->so_pcb) {	/* 如果socket插口仍然同协议相连，发送PRU_DETACH请求断开插口与协议的关联 */
		int error2 =
		    (*so->so_proto->pr_usrreq)(so, PRU_DETACH,
			(struct mbuf *)0, (struct mbuf *)0, (struct mbuf *)0);
		if (error == 0)
			error = error2;
	}
discard:
	if (so->so_state & SS_NOFDREF)
		panic("soclose: NOFDREF");
	so->so_state |= SS_NOFDREF;
	sofree(so);	/* 释放socket结构 */
	splx(s);
	return (error);
}

/*
 * Must be called at splnet...
 */
soabort(so)
	struct socket *so;
{

	return (
	    (*so->so_proto->pr_usrreq)(so, PRU_ABORT,
		(struct mbuf *)0, (struct mbuf *)0, (struct mbuf *)0));
}

soaccept(so, nam)
	register struct socket *so;
	struct mbuf *nam;
{
	int s = splnet();
	int error;

	if ((so->so_state & SS_NOFDREF) == 0)
		panic("soaccept: !NOFDREF");
	so->so_state &= ~SS_NOFDREF;
	error = (*so->so_proto->pr_usrreq)(so, PRU_ACCEPT,
	    (struct mbuf *)0, nam, (struct mbuf *)0);
	splx(s);
	return (error);
}

soconnect(so, nam)
	register struct socket *so;
	struct mbuf *nam;
{
	int s;
	int error;

	if (so->so_options & SO_ACCEPTCONN)		/* 如果socket因调用listen被标识为准备接收连接，则进程不能发起连接。*/
		return (EOPNOTSUPP);
	s = splnet();
	/*
	 * If protocol is connection-based, can only connect once.
	 * Otherwise, if connected, try to disconnect first.
	 * This allows user to disconnect by connecting to, e.g.,
	 * a null address.
	 */
	/* 由于socket设置了非阻塞标志 SS_NBIO，之前connect 调用 soconnec返回时，连接还未完成，connect直接返回了 EINPROGRESS。
	  再次调用connect时，满足if条件，说明连接已完成，直接返回EISCONN，无需再调用协议层处理操作PRU_CONNECT                                         */
	if (so->so_state & (SS_ISCONNECTED|SS_ISCONNECTING) &&
	    ((so->so_proto->pr_flags & PR_CONNREQUIRED) ||
	    (error = sodisconnect(so))))
		error = EISCONN;
	else
		error = (*so->so_proto->pr_usrreq)(so, PRU_CONNECT,
		    (struct mbuf *)0, nam, (struct mbuf *)0);	/* 调用协议层处理操作 */
	splx(s);
	return (error);
}

soconnect2(so1, so2)
	register struct socket *so1;
	struct socket *so2;
{
	int s = splnet();
	int error;

	error = (*so1->so_proto->pr_usrreq)(so1, PRU_CONNECT2,
	    (struct mbuf *)0, (struct mbuf *)so2, (struct mbuf *)0);
	splx(s);
	return (error);
}

sodisconnect(so)
	register struct socket *so;
{
	int s = splnet();
	int error;

	if ((so->so_state & SS_ISCONNECTED) == 0) {
		error = ENOTCONN;
		goto bad;
	}
	if (so->so_state & SS_ISDISCONNECTING) {
		error = EALREADY;
		goto bad;
	}
	error = (*so->so_proto->pr_usrreq)(so, PRU_DISCONNECT,
	    (struct mbuf *)0, (struct mbuf *)0, (struct mbuf *)0);
bad:
	splx(s);
	return (error);
}

#define	SBLOCKWAIT(f)	(((f) & MSG_DONTWAIT) ? M_NOWAIT : M_WAITOK)
/*
 * Send on a socket.
 * If send must go all at once and message is larger than
 * send buffering, then hard error.
 * Lock against other senders.
 * If must go all at once and not enough room now, then
 * inform user that this would block and do nothing.
 * Otherwise, if nonblocking, send as much as possible.
 * The data to be sent is described by "uio" if nonzero,
 * otherwise by the mbuf chain "top" (which must be null
 * if uio is not).  Data provided in mbuf chain must be small
 * enough to send all at once.
 *
 * Returns nonzero on error, timeout or signal; callers
 * must check for short counts if EINTR/ERESTART are returned.
 * Data and control buffers are freed on return.
 */
/* 负责处理所有socket层和协议层(各种类型的协议)之间的写操作 */
sosend(so, addr, uio, top, control, flags)
	register struct socket *so;
	struct mbuf *addr;		/* 目的地址信息 */
	struct uio *uio;		/* 待发送数据(进程发包) */
	struct mbuf *top;		/* 待发送数据(内核发包)的mbuf链。注意：top与uio不同时使用 */
	struct mbuf *control;	/* 控制信息 */
	int flags;
{
	struct proc *p = curproc;		/* XXX */
	struct mbuf **mp;
	register struct mbuf *m;
	register long space, len, resid;
	int clen = 0, error, s, dontroute, mlen;
	int atomic = sosendallatonce(so) || top;	/* 判断传入的进程数据或内核mbuf链是否一次送到协议层。进程数据看是否设置PR_ATOMIC，内核mbuf链要一次传送。*/

	if (uio)	/* 进程发包，使用该分支 */
		resid = uio->uio_resid;
	else		/* 内核发包，使用该分支 */
		resid = top->m_pkthdr.len;
	/*
	 * In theory resid should be unsigned.
	 * However, space must be signed, as it might be less than 0
	 * if we over-committed, and we must use a signed comparison
	 * of space and resid.  On the other hand, a negative resid
	 * causes us to loop sending 0-length segments to the protocol.
	 */
	if (resid < 0)	/* 要发出的数据长度小于0时，直接退出 */
		return (EINVAL);
	dontroute =
	    (flags & MSG_DONTROUTE) && (so->so_options & SO_DONTROUTE) == 0 &&
	    (so->so_proto->pr_flags & PR_ATOMIC);
	p->p_stats->p_ru.ru_msgsnd++;
	if (control)
		clen = control->m_len;
#define	snderr(errno)	{ error = errno; splx(s); goto release; }

restart:
	if (error = sblock(&so->so_snd, SBLOCKWAIT(flags)))		/* 给发送sb加锁，保证同时只能有一个进程操作该sb。 */
		goto out;

	/* *********************************************************** 差错检查、得不到发送缓存或足够的发送数据时，在此循环停留。 */
	do {
		s = splnet();
		if (so->so_state & SS_CANTSENDMORE)	/* 比如TCP连接的写道通已经被关闭时，应停止发送数据 */
			snderr(EPIPE);
		if (so->so_error)					/* 比如前一个数据报产生了一个 ICMP不可达的差错时，应停止发送数据 */
			snderr(so->so_error);
		/* 对于要发往外部的数据所有下述情况之一时，停止发送数据
			1.如果协议需要连接，但还没有为当前socket建立连接
			2.协议不需要连接，但没有提供数据发送所需的目的地址
		*/
		if ((so->so_state & SS_ISCONNECTED) == 0) {
			if (so->so_proto->pr_flags & PR_CONNREQUIRED) {
				if ((so->so_state & SS_ISCONFIRMING) == 0 &&
				    !(resid == 0 && clen != 0))
					snderr(ENOTCONN);
			} else if (addr == 0)
				snderr(EDESTADDRREQ);
		}
		space = sbspace(&so->so_snd);		/* 获得剩余可用空间，对于带外数据给与更多的空间 */
		if (flags & MSG_OOB)
			space += 1024;
		/* 1.如果是一次发送且待发送数据长度 > 发送上限长度要求，停止发送数据 2.控制报文长度 > 发送上限长度要求，同样停止发送数据 */
		if (atomic && resid > so->so_snd.sb_hiwat ||
		    clen > so->so_snd.sb_hiwat)
			snderr(EMSGSIZE);

		/* 要发送的是进程数据且剩余发送缓存不足以容纳发送数据和控制信息且满足以下任一条件时，进程挂起等待更多剩余空间
			1.要发送的数据必须一次发完，因为PR_ATOMIC类型的数据是没有边界的，sosend必须保护进程和协议层之间的边界。
			2.数据可以多次发出，但剩余发送缓存小于发送下限长度要求
			3.数据可以多次发出，但剩余发送缓存小于控制信息长度

		  如果要发送的是内核数据，由于数据已经在 mbuf缓存中了，可以忽略缓存高、低水位标记限制，因为不需要附加的缓存来保存数据。*/
		if (space < resid + clen && uio &&
		    (atomic || space < so->so_snd.sb_lowat || space < clen)) {
			if (so->so_state & SS_NBIO)	/* 如果该socket是非阻塞的，立即退出等待 */
				snderr(EWOULDBLOCK);

			/* 如果是非阻塞式发送，释放加在sb上的锁，调用sbwait等待更多可用缓存 */
			sbunlock(&so->so_snd);
			error = sbwait(&so->so_snd);/* 如果sbwait是因为有更多可用缓存返回error为0；否则非0(例如设置了等待超时时间) */
			splx(s);
			if (error)		/* 由于某些原因(例如设置了等待超时时间)，不再等待更多可用缓存，停止发送数据 */
				goto out;
			goto restart;	/* 等到了更多要发出的数据，重新开始准备发送 */
		}
		splx(s);
		mp = &top;
		space -= clen;		/* 给控制信息流出缓存空间 */

		/* *********************************************************** 把数据给协议层后，发现又有数据要发送并有缓存空间时，在此循环停留。 */
		do {
		    if (uio == NULL)
			{
				/*
				 * Data is prepackaged in "top".
				 */
				resid = 0;
				if (flags & MSG_EOR)
					top->m_flags |= M_EOR;
		    }
			else
			{
				/* *********************************************************** PR_ATOMIC被设置，数据需要在一个mbuf链中集中发出时，在此循环停留。
				当atomic被设置(内核数据或设置了PR_ATOMIC的进程数据)时，只有当有足够的缓存空间来存放整个报文时才从这个循环离开。
				通常此时传送给协议的mbuf链中包含多个mbuf。当atomic未被设置时，传送给协议的mbuf链中只包含一个mbuf */
				do
				{
					if (top == 0) {
						MGETHDR(m, M_WAIT, MT_DATA);	/* 对于进程数据，分配的mbuf空间要为struct	pkthdr 留出一部分空间 */
						mlen = MHLEN;
						m->m_pkthdr.len = 0;
						m->m_pkthdr.rcvif = (struct ifnet *)0;
					} else {
						MGET(m, M_WAIT, MT_DATA);		/* 对于内核数据，分配的mbuf空间全部用于存放要发出的数据 */
						mlen = MLEN;
					}
					/* 前面为mbuf分配的空间最多只能存储MINCLSIZE(此值默认是208字节)长度的数据，如果发送数据长度超过这个值，
					  应该为该mbuf分配一个外部簇，用来存储发送数据。下面if/else用来分别设置在使用外部簇和标准簇时，
					  要发送数据长度和剩余发送缓存空间 */
					if (resid >= MINCLSIZE && space >= MCLBYTES) {
						MCLGET(m, M_WAIT);
						if ((m->m_flags & M_EXT) == 0)	/* 分配外部簇失败，使用标准簇多次发送 */
							goto nopages;
						mlen = MCLBYTES;
#ifdef	MAPPED_MBUFS
						len = min(MCLBYTES, resid);
#else
						if (atomic && top == 0) {		/* 对于要一次发送的进程数据，要为其保留地址空间 */
							len = min(MCLBYTES - max_hdr, resid);
							m->m_data += max_hdr;
						} else
							len = min(MCLBYTES, resid);
#endif
						space -= MCLBYTES;
					} else {
		nopages:
						len = min(min(mlen, resid), space);
						space -= len;
						/*
						 * For datagram protocols, leave room
						 * for protocol headers in first mbuf.
						 */
						if (atomic && top == 0 && len < mlen)	/* 要携带地址信息且mlen没有用完时，地址尾部按sizeof(long)字节对齐 */
							MH_ALIGN(m, len);
					}
					error = uiomove(mtod(m, caddr_t), (int)len, uio);	/* 把用户要发送的数据拷贝到mbuf */
					resid = uio->uio_resid;
					m->m_len = len;
					*mp = m;			/* 在top中存放mbuf链地址，以便把发送数据交给协议时，使用top统一操作 */
					top->m_pkthdr.len += len;
					if (error)			/* 在uiomove发送数据拷贝过程中发生错误，退出发送 */
						goto release;
					mp = &m->m_next;
					if (resid <= 0) {	/* 当sosend从进程得到所有数据，跳出数据拷贝循环，发送数据给协议层 */
						if (flags & MSG_EOR)
							top->m_flags |= M_EOR;
						break;
					}
				} while (space > 0 && atomic);	/* 当PR_ATOMIC被设置时，继续拷贝数据，直到所有数据都被复制到一个mbuf链中，一次发出数据。 */
			}

		    if (dontroute)
			    so->so_options |= SO_DONTROUTE;
		    s = splnet();				/* XXX */
			/* 把要发送的数据交给下层发出 */
		    error = (*so->so_proto->pr_usrreq)(so,
			(flags & MSG_OOB) ? PRU_SENDOOB : PRU_SEND,
			top, addr, control);
		    splx(s);
		    if (dontroute)
			    so->so_options &= ~SO_DONTROUTE;

			/* 如果数据是分多次发送，控制信息只在第一次时发出 */
		    clen = 0;
		    control = 0;
		    top = 0;

		    mp = &top;
		    if (error)
				goto release;
		} while (resid && space > 0);	/* 如果还有数据要发送并有缓存空间时，重新进入数据拷贝循环，并发送数据给协议层。 */
	} while (resid);					/* 如果还有数据要发送但没有有缓存空间时，回到循环开始，等待空闲空间。 */

release:
	sbunlock(&so->so_snd);	/* 解除对该写sb的锁，唤醒所有等待使用该sb的进程。 */
out:
	if (top)
		m_freem(top);
	if (control)
		m_freem(control);
	return (error);
}

/*
 * Implement receive operations on a socket.
 * We depend on the way that records are added to the sockbuf
 * by sbappend*.  In particular, each record (mbufs linked through m_next)
 * must begin with an address if the protocol so specifies,
 * followed by an optional mbuf or mbufs containing ancillary data,
 * and then zero or more mbufs of data.
 * In order to avoid blocking network interrupts for the entire time here,
 * we splx() while doing the actual copy to user space.
 * Although the sockbuf is locked, new data may still be appended,
 * and thus we must maintain consistency of the sockbuf during that time.
 *
 * The caller may receive the data as a single mbuf chain by supplying
 * an mbuf **mp0 for use in returning the chain.  The uio is then used
 * only for the count in uio_resid.
 */
/* 负责处理所有socket层和协议层(各种类型的协议)之间的读操作 */
soreceive(so, paddr, uio, mp0, controlp, flagsp)
	register struct socket *so;
	struct mbuf **paddr;
	struct uio *uio;
	struct mbuf **mp0;
	struct mbuf **controlp;
	int *flagsp;
{
	register struct mbuf *m, **mp;
	register int flags, len, error, s, offset;
	struct protosw *pr = so->so_proto;
	struct mbuf *nextrecord;
	int moff, type;
	int orig_resid = uio->uio_resid;

	mp = mp0;
	if (paddr)
		*paddr = 0;
	if (controlp)
		*controlp = 0;
	if (flagsp)
		flags = *flagsp &~ MSG_EOR;
	else
		flags = 0;
	if (flags & MSG_OOB) {
		m = m_get(M_WAIT, MT_DATA);
		error = (*pr->pr_usrreq)(so, PRU_RCVOOB,
		    m, (struct mbuf *)(flags & MSG_PEEK), (struct mbuf *)0);
		if (error)
			goto bad;
		do {
			error = uiomove(mtod(m, caddr_t),
			    (int) min(uio->uio_resid, m->m_len), uio);
			m = m_free(m);
		} while (uio->uio_resid && error == 0 && m);
bad:
		if (m)
			m_freem(m);
		return (error);
	}
	if (mp)
		*mp = (struct mbuf *)0;
	if (so->so_state & SS_ISCONFIRMING && uio->uio_resid)
		(*pr->pr_usrreq)(so, PRU_RCVD, (struct mbuf *)0,
		    (struct mbuf *)0, (struct mbuf *)0);

restart:
	if (error = sblock(&so->so_rcv, SBLOCKWAIT(flags)))		/* 对于一个socket只属于一个进程的情况，在此是不会因为lock阻塞的 */
		return (error);
	s = splnet();

	m = so->so_rcv.sb_mb;
	/*
	 * If we have less data than requested, block awaiting more
	 * (subject to any timeout) if:
	 *   1. the current count is less than the low water mark, or
	 *   2. MSG_WAITALL is set, and it is possible to do the entire
	 *	receive operation at once if we block (resid <= hiwat).
	 *   3. MSG_DONTWAIT is not set
	 * If MSG_WAITALL is set but resid is larger than the receive buffer,
	 * we have to do the receive in sections, and thus risk returning
	 * a short count if a timeout or signal occurs after we start.
	 */
	if (m == 0 || ((flags & MSG_DONTWAIT) == 0 &&
	    so->so_rcv.sb_cc < uio->uio_resid) &&
	    (so->so_rcv.sb_cc < so->so_rcv.sb_lowat ||
	    ((flags & MSG_WAITALL) && uio->uio_resid <= so->so_rcv.sb_hiwat)) &&
	    m->m_nextpkt == 0 && (pr->pr_flags & PR_ATOMIC) == 0) {
#ifdef DIAGNOSTIC
		if (m == 0 && so->so_rcv.sb_cc)
			panic("receive 1");
#endif
		if (so->so_error) {
			if (m)
				goto dontblock;
			error = so->so_error;
			if ((flags & MSG_PEEK) == 0)
				so->so_error = 0;
			goto release;
		}
		if (so->so_state & SS_CANTRCVMORE) {
			if (m)
				goto dontblock;
			else
				goto release;
		}
		for (; m; m = m->m_next)
			if (m->m_type == MT_OOBDATA  || (m->m_flags & M_EOR)) {
				m = so->so_rcv.sb_mb;
				goto dontblock;
			}
		if ((so->so_state & (SS_ISCONNECTED|SS_ISCONNECTING)) == 0 &&
		    (so->so_proto->pr_flags & PR_CONNREQUIRED)) {
			error = ENOTCONN;
			goto release;
		}
		if (uio->uio_resid == 0)
			goto release;
		if ((so->so_state & SS_NBIO) || (flags & MSG_DONTWAIT)) {
			error = EWOULDBLOCK;
			goto release;
		}
		sbunlock(&so->so_rcv);
		error = sbwait(&so->so_rcv);
		splx(s);
		if (error)
			return (error);
		goto restart;
	}
dontblock:
	if (uio->uio_procp)
		uio->uio_procp->p_stats->p_ru.ru_msgrcv++;
	nextrecord = m->m_nextpkt;
	if (pr->pr_flags & PR_ADDR) {
#ifdef DIAGNOSTIC
		if (m->m_type != MT_SONAME)
			panic("receive 1a");
#endif
		orig_resid = 0;
		if (flags & MSG_PEEK) {
			if (paddr)
				*paddr = m_copy(m, 0, m->m_len);
			m = m->m_next;
		} else {
			sbfree(&so->so_rcv, m);
			if (paddr) {
				*paddr = m;
				so->so_rcv.sb_mb = m->m_next;
				m->m_next = 0;
				m = so->so_rcv.sb_mb;
			} else {
				MFREE(m, so->so_rcv.sb_mb);
				m = so->so_rcv.sb_mb;
			}
		}
	}
	while (m && m->m_type == MT_CONTROL && error == 0) {
		if (flags & MSG_PEEK) {
			if (controlp)
				*controlp = m_copy(m, 0, m->m_len);
			m = m->m_next;
		} else {
			sbfree(&so->so_rcv, m);
			if (controlp) {
				if (pr->pr_domain->dom_externalize &&
				    mtod(m, struct cmsghdr *)->cmsg_type ==
				    SCM_RIGHTS)
				   error = (*pr->pr_domain->dom_externalize)(m);
				*controlp = m;
				so->so_rcv.sb_mb = m->m_next;
				m->m_next = 0;
				m = so->so_rcv.sb_mb;
			} else {
				MFREE(m, so->so_rcv.sb_mb);
				m = so->so_rcv.sb_mb;
			}
		}
		if (controlp) {
			orig_resid = 0;
			controlp = &(*controlp)->m_next;
		}
	}
	if (m) {
		if ((flags & MSG_PEEK) == 0)
			m->m_nextpkt = nextrecord;
		type = m->m_type;
		if (type == MT_OOBDATA)
			flags |= MSG_OOB;
	}
	moff = 0;
	offset = 0;
	while (m && uio->uio_resid > 0 && error == 0) {
		if (m->m_type == MT_OOBDATA) {
			if (type != MT_OOBDATA)
				break;
		} else if (type == MT_OOBDATA)
			break;
#ifdef DIAGNOSTIC
		else if (m->m_type != MT_DATA && m->m_type != MT_HEADER)
			panic("receive 3");
#endif
		so->so_state &= ~SS_RCVATMARK;
		len = uio->uio_resid;
		if (so->so_oobmark && len > so->so_oobmark - offset)
			len = so->so_oobmark - offset;
		if (len > m->m_len - moff)
			len = m->m_len - moff;
		/*
		 * If mp is set, just pass back the mbufs.
		 * Otherwise copy them out via the uio, then free.
		 * Sockbuf must be consistent here (points to current mbuf,
		 * it points to next record) when we drop priority;
		 * we must note any additions to the sockbuf when we
		 * block interrupts again.
		 */
		if (mp == 0) {
			splx(s);
			error = uiomove(mtod(m, caddr_t) + moff, (int)len, uio);
			s = splnet();
		} else
			uio->uio_resid -= len;
		if (len == m->m_len - moff) {
			if (m->m_flags & M_EOR)
				flags |= MSG_EOR;
			if (flags & MSG_PEEK) {
				m = m->m_next;
				moff = 0;
			} else {
				nextrecord = m->m_nextpkt;
				sbfree(&so->so_rcv, m);
				if (mp) {
					*mp = m;
					mp = &m->m_next;
					so->so_rcv.sb_mb = m = m->m_next;
					*mp = (struct mbuf *)0;
				} else {
					MFREE(m, so->so_rcv.sb_mb);
					m = so->so_rcv.sb_mb;
				}
				if (m)
					m->m_nextpkt = nextrecord;
			}
		} else {
			if (flags & MSG_PEEK)
				moff += len;
			else {
				if (mp)
					*mp = m_copym(m, 0, len, M_WAIT);
				m->m_data += len;
				m->m_len -= len;
				so->so_rcv.sb_cc -= len;
			}
		}
		if (so->so_oobmark) {
			if ((flags & MSG_PEEK) == 0) {
				so->so_oobmark -= len;
				if (so->so_oobmark == 0) {
					so->so_state |= SS_RCVATMARK;
					break;
				}
			} else {
				offset += len;
				if (offset == so->so_oobmark)
					break;
			}
		}
		if (flags & MSG_EOR)
			break;
		/*
		 * If the MSG_WAITALL flag is set (for non-atomic socket),
		 * we must not quit until "uio->uio_resid == 0" or an error
		 * termination.  If a signal/timeout occurs, return
		 * with a short count but without error.
		 * Keep sockbuf locked against other readers.
		 */
		while (flags & MSG_WAITALL && m == 0 && uio->uio_resid > 0 &&
		    !sosendallatonce(so) && !nextrecord) {
			if (so->so_error || so->so_state & SS_CANTRCVMORE)
				break;
			error = sbwait(&so->so_rcv);
			if (error) {
				sbunlock(&so->so_rcv);
				splx(s);
				return (0);
			}
			if (m = so->so_rcv.sb_mb)
				nextrecord = m->m_nextpkt;
		}
	}

	if (m && pr->pr_flags & PR_ATOMIC) {
		flags |= MSG_TRUNC;
		if ((flags & MSG_PEEK) == 0)
			(void) sbdroprecord(&so->so_rcv);
	}
	if ((flags & MSG_PEEK) == 0) {
		if (m == 0)
			so->so_rcv.sb_mb = nextrecord;
		if (pr->pr_flags & PR_WANTRCVD && so->so_pcb)
			(*pr->pr_usrreq)(so, PRU_RCVD, (struct mbuf *)0,
			    (struct mbuf *)flags, (struct mbuf *)0,
			    (struct mbuf *)0);
	}
	if (orig_resid == uio->uio_resid && orig_resid &&
	    (flags & MSG_EOR) == 0 && (so->so_state & SS_CANTRCVMORE) == 0) {
		sbunlock(&so->so_rcv);
		splx(s);
		goto restart;
	}
		
	if (flagsp)
		*flagsp |= flags;
release:
	sbunlock(&so->so_rcv);
	splx(s);
	return (error);
}

soshutdown(so, how)
	register struct socket *so;
	register int how;
{
	register struct protosw *pr = so->so_proto;

	how++;
	if (how & FREAD)	/* 读通道，丢弃所有进程还没有读走的数据以及调用 shutdown之后到达的数据。*/
		sorflush(so);
	if (how & FWRITE)	/* 写通道，对于TCP，所有剩余的数据将被发送，发送完成后发送FIN关闭TCP连接的写通道。 */
		return ((*pr->pr_usrreq)(so, PRU_SHUTDOWN,
		    (struct mbuf *)0, (struct mbuf *)0, (struct mbuf *)0));
	return (0);
}

/* 释放接收缓存数据 */
sorflush(so)
	register struct socket *so;
{
	register struct sockbuf *sb = &so->so_rcv;
	register struct protosw *pr = so->so_proto;
	register int s;
	struct sockbuf asb;

	sb->sb_flags |= SB_NOINTR;			/* 设置SB_NOINTR，当中断出现时，下面sblock不返回 */
	(void) sblock(sb, M_WAITOK);
	s = splimp();		/* 在修改插口状态时，splimp阻塞网络中断和协议处理，因为协议层在接收到进入的分组时可能要访问接收缓存。*/
	socantrcvmore(so);	/* 设置socket拒绝接收进入的分组 */
	sbunlock(sb);
	asb = *sb;
	bzero((caddr_t)sb, sizeof (*sb));	/* 清除原始的sockbuf结构，使得接收队列为空 */
	splx(s);			/* 恢复中断 */

	/* 释放控制mbuf。
	  当shutdown被调用时，存储在接收队列中的控制信息可能引用了一些内核资源。通过sockbuf结构的副本中的sb_mb仍然可以访问mbuf链。
	  如果协议支持访问权限，且注册了一个dom_dispose函数，则调用该函数来释放这些资源。 */
	if (pr->pr_flags & PR_RIGHTS && pr->pr_domain->dom_dispose)
		(*pr->pr_domain->dom_dispose)(asb.sb_mb);
	sbrelease(&asb);	/* 释放接收队列中的所有mbuf时，丢弃所有调用shutdown时还没有被处理的数据。*/
}

sosetopt(so, level, optname, m0)
	register struct socket *so;
	int level, optname;
	struct mbuf *m0;
{
	int error = 0;
	register struct mbuf *m = m0;

	if (level != SOL_SOCKET) {
		if (so->so_proto && so->so_proto->pr_ctloutput)
			return ((*so->so_proto->pr_ctloutput)
				  (PRCO_SETOPT, so, level, optname, &m0));
		error = ENOPROTOOPT;
	} else {
		switch (optname) {

		case SO_LINGER:
			if (m == NULL || m->m_len != sizeof (struct linger)) {
				error = EINVAL;
				goto bad;
			}
			so->so_linger = mtod(m, struct linger *)->l_linger;
			/* fall thru... */

		case SO_DEBUG:
		case SO_KEEPALIVE:
		case SO_DONTROUTE:
		case SO_USELOOPBACK:
		case SO_BROADCAST:
		case SO_REUSEADDR:
		case SO_REUSEPORT:
		case SO_OOBINLINE:
			if (m == NULL || m->m_len < sizeof (int)) {
				error = EINVAL;
				goto bad;
			}
			if (*mtod(m, int *))
				so->so_options |= optname;
			else
				so->so_options &= ~optname;
			break;

		case SO_SNDBUF:
		case SO_RCVBUF:
		case SO_SNDLOWAT:
		case SO_RCVLOWAT:
			if (m == NULL || m->m_len < sizeof (int)) {
				error = EINVAL;
				goto bad;
			}
			switch (optname) {

			case SO_SNDBUF:
			case SO_RCVBUF:
				if (sbreserve(optname == SO_SNDBUF ?
				    &so->so_snd : &so->so_rcv,
				    (u_long) *mtod(m, int *)) == 0) {
					error = ENOBUFS;
					goto bad;
				}
				break;

			case SO_SNDLOWAT:
				so->so_snd.sb_lowat = *mtod(m, int *);
				break;
			case SO_RCVLOWAT:
				so->so_rcv.sb_lowat = *mtod(m, int *);
				break;
			}
			break;

		case SO_SNDTIMEO:
		case SO_RCVTIMEO:
		    {
			struct timeval *tv;
			short val;

			if (m == NULL || m->m_len < sizeof (*tv)) {
				error = EINVAL;
				goto bad;
			}
			tv = mtod(m, struct timeval *);
			if (tv->tv_sec > SHRT_MAX / hz - hz) {
				error = EDOM;
				goto bad;
			}
			val = tv->tv_sec * hz + tv->tv_usec / tick;

			switch (optname) {

			case SO_SNDTIMEO:
				so->so_snd.sb_timeo = val;
				break;
			case SO_RCVTIMEO:
				so->so_rcv.sb_timeo = val;
				break;
			}
			break;
		    }

		default:
			error = ENOPROTOOPT;
			break;
		}
		if (error == 0 && so->so_proto && so->so_proto->pr_ctloutput) {
			(void) ((*so->so_proto->pr_ctloutput)
				  (PRCO_SETOPT, so, level, optname, &m0));
			m = NULL;	/* freed by protocol */
		}
	}
bad:
	if (m)
		(void) m_free(m);
	return (error);
}

sogetopt(so, level, optname, mp)
	register struct socket *so;
	int level, optname;
	struct mbuf **mp;
{
	register struct mbuf *m;

	if (level != SOL_SOCKET) {
		if (so->so_proto && so->so_proto->pr_ctloutput) {
			return ((*so->so_proto->pr_ctloutput)
				  (PRCO_GETOPT, so, level, optname, mp));
		} else
			return (ENOPROTOOPT);
	} else {
		m = m_get(M_WAIT, MT_SOOPTS);
		m->m_len = sizeof (int);

		switch (optname) {

		case SO_LINGER:
			m->m_len = sizeof (struct linger);
			mtod(m, struct linger *)->l_onoff =
				so->so_options & SO_LINGER;
			mtod(m, struct linger *)->l_linger = so->so_linger;
			break;

		case SO_USELOOPBACK:
		case SO_DONTROUTE:
		case SO_DEBUG:
		case SO_KEEPALIVE:
		case SO_REUSEADDR:
		case SO_REUSEPORT:
		case SO_BROADCAST:
		case SO_OOBINLINE:
			*mtod(m, int *) = so->so_options & optname;
			break;

		case SO_TYPE:
			*mtod(m, int *) = so->so_type;
			break;

		case SO_ERROR:
			*mtod(m, int *) = so->so_error;
			so->so_error = 0;
			break;

		case SO_SNDBUF:
			*mtod(m, int *) = so->so_snd.sb_hiwat;
			break;

		case SO_RCVBUF:
			*mtod(m, int *) = so->so_rcv.sb_hiwat;
			break;

		case SO_SNDLOWAT:
			*mtod(m, int *) = so->so_snd.sb_lowat;
			break;

		case SO_RCVLOWAT:
			*mtod(m, int *) = so->so_rcv.sb_lowat;
			break;

		case SO_SNDTIMEO:
		case SO_RCVTIMEO:
		    {
			int val = (optname == SO_SNDTIMEO ?
			     so->so_snd.sb_timeo : so->so_rcv.sb_timeo);

			m->m_len = sizeof(struct timeval);
			mtod(m, struct timeval *)->tv_sec = val / hz;
			mtod(m, struct timeval *)->tv_usec =
			    (val % hz) / tick;
			break;
		    }

		default:
			(void)m_free(m);
			return (ENOPROTOOPT);
		}
		*mp = m;
		return (0);
	}
}

sohasoutofband(so)
	register struct socket *so;
{
	struct proc *p;

	if (so->so_pgid < 0)
		gsignal(-so->so_pgid, SIGURG);
	else if (so->so_pgid > 0 && (p = pfind(so->so_pgid)) != 0)
		psignal(p, SIGURG);
	selwakeup(&so->so_rcv.sb_sel);
}
